«1 MONTHLY. [>o 
XXII. 
COLOMBO, NOVEMBER 1st, 190-2. 
No. 5. 
FOLIAR PERIODICITY IN CEYLON. 
BV HEKBEIIT WIIIGHT, A.R.C.S., F.L.S, 
Paper read Uforc the British Asuociation for lit'. Ad- 
vancement of Science, Belfast, Septemher. 1902. B"- 
printed by "Tropical Agriculturist," Nov. 1903. 
f ^m,:-,^ - ^...:=r-rv^^ - ? subject of foliar perioaicity 
j|^^?S==^" 1 fT^^J '"'^ tropics i3 of fsp:cial iti- 
SlfmMYi If'-viiM terest (rt) in virtue of the assist- 
ance it gives to tlie study of 
tiie histological differentiation 
of the secondary xylem, (h) in 
consequence of the plants having 
leas resistance than in tem- 
perate zones, and (c) because erroneous ooaceptions 
of the scarcity of deciduous tropical trees exist in 
the minds of many botanists. 
The high temperature and humidity of the air 
in most parts of Ceylon is such as to allow nearly 
continuous growth of the arborescent vegetation. la 
consequence of this, there is no period analogous 
to the winter of a temperate zone when almost 
every species becomes leafless and remains so until 
the spring time arrives. The majority of the 
trees in Ceylon are of an evergreen nature, and 
even in the deciduous forms there ia considerable 
irregularity in the periodicity of leaf fall and pro- 
duction, 
Deciduous Trees.— In Ceylon, there is no relation- 
ship between deciduous and allied species. The same 
genus may or may not contain deciduous species, or as 
in the genera Terminalia, Ficus, Sterculia, Stereosper- 
mnm, and many others, there may be a very large per- 
centage of the species decid uous. Some natural 
ordersj as for instance the SapotaceEO and Ebena- 
ceee, are peculiar in that only one or two species 
are other than evergreen, and not a single natural 
order can be quoted which has a high percentage 
of decHuous species. Neveretheless, though this 
investigation is quite young, I have obtained nearly 
SOO fikcies of Ceylon trees which pass through a 
deciduous phase at recurring periods of time. It 
is worthy of note that though different specimens 
of the sacue species show every variability in the 
period of time at which they drop their leaves and 
piodiice new foliage, yet the same tree passes 
through this phase at exactly corresponding times 
from year to 3 ear. 
In studying the behaviour of our deciduous trees 
the most usual conclusion is that no law and order 
prevails, and any tree drops its leaves how and 
wheu it chooses. There are, however, certain 
features which point to a climatic response, and 
others which indicate that the personal or interval 
forces are the chief agencies at work. It can be defi- 
nitely stated that the majority of our deciduous species 
show a response to climate, in so far that they 
do, in climates similar to that prevailing at 
Peradeniya, drop all their leaves and remain leaf- 
less during our hottest and driest season. This 
hot dry period extends from January to April or 
May, and the leafless trees of Bcmbas mala- 
barium, D.G., Eriodendrou anfractuosum, D.C., 
Spondias mangifera, Willd.i Stereo'permnm chele- 
noides, D.C., Fi:us Arnottiana, Mig., Derris 
robusta, Benth., Careya arboreft, Gaertn, 
Fi3U9 religiosa, L., d'ataevae Esxburghii, Br., and 
very many other species, give a characteristic 
barren appearance to the arborescent vegetation. 
Very many species undergo defoliation, and 
this does not occur during the dry part of each 
monsoon but only during the time stated. The 
deciduous trees seem, therefore, only to recognise 
one hot dry period of three to four months as 
against the alternating dry and wet months of the 
remainder of the year. Further, every tree of 
Terminalia Catappa undergoes a complete change, 
of leaf during the dry part of each monsoon, and 
other species, I suspect, undergo foliar repletion twice 
every year. In addition to these we have some 
species, not native, which though they drop all 
their leaves and regain complete foliage at one 
time of the year, also suffer partial falls and pro- 
ductions at {other times of the year. Pithecolobium 
Saman, Benth.; Stereospermura chelenoide=. 
Instances of acclimatisation are well known, but 
there are also some species which do not appear 
capable of readily aooommodatinp themselves and 
